docs: def _appendstore(self, store):
          """Join another store on to the end of this one."""
          if not store.bitlength:
              return
          # Set new array offset to the number of bits in the final byte of current array.
          store = offsetcopy(store, (self.offset + self.bitlength) % 8)
          if store.offset:
              # first do the byte with the join.
              joinval = (self._rawarray.pop() & (255 ^ (255 >> store.offset)) |
                         (store.getbyte(0) & (255 >> store.offset)))
              self._rawarray.append(joinval)
              self._rawarray.extend(store._rawarray[1:])
          else:
              self._rawarray.extend(store._rawarray)
          self.bitlength += store.bitlength